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1. C PROGRAMMING
Functions
By,
Mr. Shekharkumar

2. What is Function?
• A function is a block of code that performs a specific task.
• A function only runs when it is called.
• You can pass data, known as parameters, into a function.
• Functions are used to perform certain actions, and they are important for
reusing code: Define the code once, and use it many times.

3. Types of function
• There are two types of function in C programming:
1. Standard library functions (Pre-Defined Functions)
2. User-defined functions

4. 1. Standard library functions (Pre-Defined Functions)
• The standard library functions are built-in functions in C programming.
• These functions are defined in header files. For example,
The printf() is a standard library function to display formatted output to the
screen. This function is defined in the stdio.h header file. Hence to use printf()
function, we need to include the stdio.h header file using #include <stdio.h>.
The sqrt() function calculates the square root of a number. The function is
defined in the math.h header file

5. 2. User-defined functions
• User-defined functions are a block of code written by the user to
perform a specific action. A user-defined function has a return type,
a function name, parameters, and body of the function. Function can
be called using the unique name of the function followed by function
parameters passed inside round brackets ().

6. Advantages of user-defined function
The program will be easier to understand, maintain and debug.
Reusable codes that can be used in other programs
A large program can be divided into smaller modules. Hence, a large
project can be divided among many programmers.

8. How function works
• The execution of a C program begins from the main() function
• When the compiler encounters functionname() control of the program jumps
to void functionname()
• And, the compiler starts executing the codes inside functionname().
• The control of the program jumps back to the main() function once
code inside the function definition is executed.

9. #include <stdio.h>
int addNumbers(int a, int b); // function prototype
int addNumbers(int a, int b) // function definition
{
int result;
result = a+b;
return result; // return statement
}
void main()
{
int n1,n2,sum;
printf("Enters two numbers: ");
scanf("%d %d",&n1,&n2);
sum = addNumbers(n1, n2); // function call
printf("sum = %d",sum);
}
Example of user-defined function